The log style ones I've seen on eBay are pretty crappy in materials, machining and flow, so I would steer clear of those. Equal length isn't as critical with turbo setups as with N/A engines, but if they are massively different it will still have a negative effect.
Is your manifold braced at all? It could be the fact that there isn't anything to support the weight of the turbo and bracing it properly might fix your issue. Otherwise I would say your best bet would be to bite the bullet and get a simple steam pipe manifold made up, and you'll never have any more issues.